In a fifth-generation mobile communication system, in order to realize increase in gain in a high frequency range or increase in system throughput using an antenna array (a multi-element antenna) including a plurality of antenna elements, research and development have been conducted. For example, beam tracking technology in which a wireless terminal that moves is caused to track a beam by beam-forming (BF) using a multi-element antennal has been examined.
It is possible to narrow down a beam in a specific direction by performing BF using a multi-element antenna and thus achieve a high gain. On the other hand, when a wireless terminal goes off from the direction of the beam, reception characteristics are deteriorated. If a beam width is narrow, a risk that a wireless terminal goes off from the direction of a beam increases. However, when a beam (a broad beam) with a wide beam width is used, a risk that a wireless terminal goes off from the direction of a beam is reduced.
Note that a method in which the number of antenna elements is increased to increase a diversity gain and thus improve a signal-to-noise ratio (SNR) of a receiver has been proposed. In this method, first and second representative data streams which have been coded using a Walsh code are transmitted from first and second antenna groups arranged apart from one another by a distance that is ten times or larger than a carrier wavelength, respectively.
Examples of the related art include Japanese Laid-open Patent Publication No. 2001-237750.